n = eval(input())
pm = 1 #用于变换正负号
s = 0 #用于保存结果
for i in range(1,n+1):
    # 分析分子和分母数列的规律
    numerator = i
    denominator = 2*i - 1
    s += pm * numerator / denominator

    pm *= -1 #变换正负号
print("{:.3f}".format(s))
